Severe valvulitis owing to acute Kawasaki disease leading to severe mitral regurgitation is a rare event in infants. Further, there is less information about underlying ruptured mitral chordae tendineae causing severe mitral regurgitation. We encountered ruptured mitral chordae tendineae in three female patients after Kawasaki disease. The age at the onset of Kawasaki disease ranged from 3 to 8 months, and detection of ruptured mitral chordae tendineae was from 24 to 90 days. Two patients had acute heart failure, and one was asymptomatic. One patient underwent mitral annuloplasty, and the others responded to medication. These ruptured mitral chordae tendineae occurred after the remission of the initial acute Kawasaki disease, in the early course and the convalescent of acute Kawasaki disease. Further, the recurrent fever was also detected in them. The ruptured mitral chordae tendineae in an infant within 6 months can be detected by systolic heart murmur around the convalescent stage of acute Kawasaki disease, although the prevalence is very low.